A conventional and well known contactor device is shown in the closed condition in FIG. 6 and in the open condition in FIG. 7. As shown in FIGS. 6 and 7, the conventional contactor device consists of a U-shaped fixed contactor 2 provided with an upper leg portion having a fixed contact point 1 provided thereon with solder or the like, a movable contact point 3 and at its other end with a U-shaped indent 4a. The movable contact point 3 is adapted to come in contact with the fixed contact point 1 and the movable contactor 4 extends in parallel with the upper leg portion of the fixed contactor 2 when the contactor device is closed. A dielectric holder 5 is oscillatably supported and supports in a rotatably journalled manner the other end of the movable contactor 4. A contacting or compression spring 7 is installed between the dielectric holder 5 and the indent 4a of the movable contactor 4 through a pin 6 to provide the force in the direction shown by an arrow in FIG. 6. This force produces counterclockwise moment around the journal of the movable contactor 4 to give contact pressure between the fixed contact point 1 and the movable contact point 3. An elastic conduit 8 is connected to the movable contactor 4.
A current breaking operation in response to a short-circuit is carried out in the conventional contactor device as follows. When the contactor device is in its closed condition and a high current in the short-circuit range flows through the fixed contactor 2 and the movable contactor 4 as shown in FIG. 6, the high current generates a magnetic repelling force F1. This causes the movable contactor 4 to rotate clockwise and the indent 4a to displace. Consequently, the point of application of the force of the compression spring 7 is shifted as shown in FIG. 7 to accelerate the clockwise rotation, and the fixed contact point 1 and the movable contact point 3 are instantaneously separated in order to open the contactor device as shown in FIG. 7.
However, in a closing motion of the conventional contactor device, the movable contact point 3 strikes or collides with the fixed contact point 1 as the movable contactor 4 and the fixed contactor 2 are instantaneously closed. This generates a shocking force and causes the compression spring 7 to vibrate. As a result, the point of application by pin 6 may be shifted for an instant to its former position, the open condition, and causes the clockwise rotation of the movable contactor 4, which results in an instantaneous separation of the movable contactor 4 from the fixed contactor 1. This causes undesirable open-phase condition. In order to prevent the contactor device from instantaneously separating, it is necessary to determine accurately the force of the compression spring 7 in view of the strength of the shocking force which will be generated.
When high shocking force is generated in a closing motion of the conventional contactor device, the contact pressure provided by the movable contactor 4 must be kept higher than the shocking force by increasing the force of the compression spring 7, and the magnetic repelling force F1 is required to be furthermore longer than this increased contact pressure. This causes the current-limiting start current value to be disadvantageously high. Consequently, it has been difficult to manufacture economically a small-sized circuit breaker provided with an excellent current-limiting characteristic.